1. Field of the Invention
The present invention relates to a method and a device for ascertaining the rotor temperature of a permanent-magnet synchronous machine, in which a first estimate of the rotor temperature is ascertained as a function of a remanent flux density of permanent magnets contained in a rotor of the synchronous machine.
2. Description of the Related Art
In permanent-magnet synchronous machines, the permanent magnets of the rotor are usually the components most sensitive to temperature because if the temperature even briefly exceeds the Curie temperature of the magnetic material used, it will cause damage to the magnets, in particular loss of their magnetization. Therefore, temperature monitoring of the rotor of the synchronous machine is advisable to protect the permanent magnets, so that the synchronous machine may be deactivated, e.g., shortly before reaching the Curie temperature.
Monitoring of the rotor temperature is technically complex due to the rotor movement. Known methods therefore propose ascertaining the rotor temperature from the more easily detectable electrical operating variables of the synchronous machine instead of a direct temperature measurement in the rotor.
Such a method is known from published German patent application document DE 102 54 295 A1 and utilizes the effect whereby the remanent flux density of the permanent magnets of the rotor depends on their temperature or on the rotor temperature. Consequently, the amplitude of the synchronous internal voltage of the synchronous machine is a function of the rotor temperature. The known method has the disadvantage that the rotor temperature is ascertained on the basis of a linear model, which is valid only in a restricted operating range of the synchronous machine due to magnetic saturation effects, among other things, and offers inadequate precision for many applications.